The present invention relates to a glass panel including a pair of glass sheets disposed in opposition to each other with forming a gap therebetween, peripheral edges of the glass sheets being directly bonded together by metal material so as to seal the gap gas-tightly.
Conventionally, a glass panel of the mentioned type, as shown in FIG. 7, includes a pair of glass sheets 1A, 1B disposed in opposition to each other with forming a gap V therebetween and metal solder 20 is charged in a molten state between the peripheral edges of the opposed glass sheets 1A, 1B, so that the glass sheets 1 are directly bonded together with subsequent solidification of the metal solder (see the international publication WO 00/58234 for example). And, no special attention has been paid to the condition on the surfaces of the glass sheets at the bonding faces of the glass sheets to be bonded to the metal material.
Incidentally, in general, the glass and molten glass have a large contact angle, i.e. poor wettability, relative to each other. Then, it may be said that these are materials difficult to be bonded to each other. Further, it is known that the greater the degree of unevenness in the glass surface, the more conspicuously this tendency shows.
Therefore, in the case of such conventional glass panel above, if the glass sheet is provided, at its bonding face, with a function additive film such as a low-radiation film made of e.g. stannic oxide, or if the glass sheet is a frosted glass sheet having frosting treatment in its bonding face, there exists a large degree of surface unevenness in its bonding face. So that, poor wettability appears conspicuously at the boding faces between the glass sheets and the molten metal, whereby sufficient bonding condition therebetween cannot be obtained. That is, it becomes impossible to maintain the gas tightness in the gap between the glass sheets or the glass sheets can even be separated from each other.
Accordingly, an object of the present invention is to provide a glass panel which overcomes the above-described problem and with which the bonding performance provided by the metal material between the glass sheets can be secured easily, thus achieving sufficient bonding strength at the bonding portions and high gas tightness.
According to the characterizing feature of the present invention relating to claim 1, a glass panel includes a pair of glass sheets 1A, 1B disposed in opposition to each other with forming a gap V therebetween, the peripheral edges of the opposed glass sheets 1A, 1B being directly bonded to each other by metal material 5, wherein bonding faces 1Aa in the opposed surfaces of the glass sheets 1A, 1B to be bonded to the metal material 5 are worked so as to obtain an average surface roughness below 30 nm.
With the characterizing feature of the invention relating to claim 1, it becomes possible to maintain high wettability between the glass sheets and the metal material at the bonding faces 1Aa, thereby to ensure bonding performance therebetween required for the glass panel.
This effect has been confirmed based on the finding obtained from an experiment conducted by the inventor (see the experiment results described in the embodiment).
That is, as described hereinbefore, the glass sheet and the metal material have a large contact angle, hence, poor wettability relative to each other. In addition, if the bonding face of the glass sheet relative to the metal material has significant surface unevenness, the bonding difficulty will further increase. Then, by setting the average surface roughness of the bonding face of the glass sheet below 30 nm, appropriate bonding strength for the glass sheets may be maintained and the gas tightness in the gap between the glass sheets may be maintained also.
According to the characterizing feature of the present invention relating to claim 2, the bonding faces 1Aa in the opposed surfaces of the glass sheets 1A, 1B to be bonded to the metal material 5 have an average surface roughness equal to or less than 15 nm.
With the characterizing feature of the invention relating to claim 2, it becomes possible to maintain even higher wettability between the glass sheets and the metal material at the bonding faces a, thereby to ensure even better bonding performance therebetween required for the glass panel.
This effect has been confirmed based on the finding from the experiment conducted by the inventor (see the experiment results described in the embodiment).
According to the characterizing feature of the present invention relating to claim 3, as shown in FIG. 2 for example, at least one glass sheet 1A of the two glass sheets 1 is a function-added glass sheet including a function additive film F on the side thereof facing the other glass sheet 1B.
With the characterizing feature of the invention relating to claim 3, in addition to the function/effect achieved by the invention relating to claim 1 or 2, it is possible to provide the glass panel with the function obtained by the function additive film.
For instance, if the function additive film is a function additive film having low-radiation function having a low radiation, it is possible to reduce the heat loss through the glass panel, whereby the heat insulating effect of the glass panel may be enhanced.
Further, the function additive film is not limited to the low-radiation film described above. This function additive film may be freely selected as such function additive film having a variety of functions of heat absorption, heat reflection, UV absorption, etc.
When such function additive film has a significant unevenness, it used to be difficult to bond this with metal material. With the present invention, however, by finishing the bonding faces with the predetermined average surface roughness specified above, it is possible to ensure sufficient bonding condition, hence obtaining a glass panel having the required gas tightness in its gap.
According to the characterizing feature of the present invention relating to claim 4, at least one glass sheet 1A of the two glass sheets 1 is a frosted glass sheet having frost working on the side thereof facing the other glass sheet 1B.
With the characterizing feature of the invention relating to claim 4, in addition to the function/effect achieved by the invention relating to claim 1 or 2, it is possible to provide the glass panel with the function of frosted glass.
For instance, it becomes possible to form a good-looking glass panel added with the blind function while allowing transmission of soft diffused light.
The surface with such frost working has a relatively large unevenness. Hence, it was substantially difficult for the prior art to bond it with metal material. However, by finishing the bonding faces with the predetermined average surface roughness specified above, it is possible to ensure sufficient bonding condition, hence obtaining a glass panel having the required gas tightness in its gap. Here, as means for adapting the bonding faces to the predetermined average surface roughness specified above, this may be done by effecting an operation for reducing the average surface roughness of the bonding face after its frost working. Alternatively, this is also possible by effecting the frost working on the portions thereof excluding the bonded faces or not effecting the frost working on the bonding faces at all or limiting the degree of frost working to be provided on the bonding faces so that the bonding faces may maintain the above-specified average surface roughness.
According to the characterizing feature of the present invention relating to claim 5, the bonding faces 1Aa of the glass sheets 1 relative to the metal material 5 has its average surface roughness adjusted by a surface working comprising a mechanical polishing, a chemical polishing or combination thereof
With the characterizing feature of the invention relating to claim 5, in addition to the function/effect achieved by the invention relating to any one of claims 1-4, it is possible to obtain substantially desired average surface roughness by appropriately selecting the polishing method or appropriately setting the polishing condition. Consequently, with a simple process, the machining accuracy may be improved.